Method for surface treatment, use of an additive and surface treatment agent

Abstract

A method for the surface treatment of workpieces by means of abrasive media, and a surface treatment composition. The method comprises the steps of providing a treatment tool, providing an abrasive medium, supplying a workpiece having a surface to be treated, surface treating the workpiece, involving removal of material and producing waste products, and processing the waste products, wherein at least one of said steps comprises adding an additive to lower a self-ignition tendency on the part of the waste products, the additive comprising a salt, composed of a carbonate and/or of a halogen anion.

Claims

1. A method for the surface treatment of workpieces by means of abrasive media, comprising the steps of: providing a treatment tool; providing an abrasive medium containing lipids; supplying a workpiece having a metal surface to be treated, wherein the metal surface to be treated is selected from the group consisting of magnesium, magnesium alloys, aluminum, aluminum alloys, titanium, titanium alloys, zinc and zinc alloys; surface treating the workpiece, involving removal of material and producing waste products containing lipids; adding a self-ignition inhibiting additive to lower a self-ignition tendency of the waste products that are formed in the step of surface treating the workpiece, the additive comprising a salt, wherein the salt is composed of at least one of a carbonate and a halogen anion; and processing the waste products.

2. The method as claimed in claim 1, wherein the step of processing the waste products comprises wetting the waste products.

3. The method as claimed in claim I, wherein the salt is selected from the group consisting of sodium carbonate, potassium carbonate, and sodium fluoride.

4. The method as claimed in claim 1, wherein the salt comprises a fluoride.

5. The method as claimed in claim 1, wherein the processing of the waste products is carried out in a wet separator which generates a wet waste.

6. The method as claimed in claim 5, wherein the additive is admixed within the wet separator or to the wet waste.

7. The method as claimed in claim 1, wherein the processing of the waste products comprises briquetting, and wherein the additive is added before the briquetting.

8. The method as claimed in claim 1, wherein the treatment tool is one or more of a grinding disk, a brushing disk, a polishing disk, a machining tool, and a blasting system.

9. The method as claimed in claim 1, wherein the treatment tool is one or more of a grinding disk, a brushing disk, a machining tool, and a polishing disk, and wherein the additive is introduced into or applied to the treatment tool.

10. The method as claimed in claim 1, wherein the abrasive medium is one or more of a polishing composition, a brushing composition, a blasting medium, a cutting material, and a grinding composition.

11. The method as claimed in claim 10, wherein the additive is added to the abrasive medium.

12. The method as claimed in claim 1, wherein the salt forms less than 10 wt % but more than 0.01 wt % of the abrasive composition.

13. The method as claimed in claim 1, wherein the lipids in the abrasive medium are selected from a group consisting of fats, oils, and waxes.

14. The method as claimed in claim 1, wherein the additive is admixed to the abrasive medium before surface treating the workpiece.

15. The method as claimed in claim 1, wherein the additive is admixed to the treatment tool.

16. The method as claimed in claim 1, wherein the additive is admixed with the waste products.

17. A method for polishing workpieces with abrasive media while lowering a self-ignition tendency of the waste products comprising: providing a polishing tool; providing an abrasive medium containing lipids; supplying a workpiece having a metal surface to be treated, wherein the metal surface to be treated is selected from the group consisting of magnesium, magnesium alloys, aluminum, aluminum alloys, titanium, titanium alloys, zinc and zinc alloys; polishing the workpiece, involving removal of material and producing waste products containing lipids; and processing the waste products; wherein the step of processing the waste products comprises adding a self-ignition inhibiting additive to the waste products formed in the step of polishing the workpiece, and wherein the additive comprises a salt composed of at least one of a carbonate and a halogen anion.

18. The method as claimed in claim 17, wherein the lipids in the abrasive medium are selected from a group consisting of fats, oils, and waxes.

19. A method for surface treatment of workpieces comprising: providing a treatment tool; providing an abrasive medium; supplying a workpiece having a surface to be treated, wherein the metal surface to be treated is selected from the group consisting of magnesium, magnesium alloys, aluminum, aluminum alloys, titanium, titanium alloys zinc and zinc alloys; surface treating the workpiece, involving removal of material from the workpiece and producing a waste product, the waste product containing lipids; adding a self-ignition inhibiting additive to lower a self-ignition tendency of the waste product that is formed in the step of surface treating of the workpiece, the additive comprising a salt, wherein the salt includes at least one of a carbonate and a halogen anion; and processing the waste products.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features, properties, and advantages of the invention will become apparent from the description hereinafter of exemplary embodiments, with reference to the drawings. These exemplary embodiments are purely illustrative and do not limit the subject matter of the invention.

(2) Reference is made to the appended figures, which show the following:

(3) FIG. 1 illustrates, using a block diagram, an exemplary embodiment of a method for the surface treatment of workpieces;

(4) FIG. 2 is a graph illustrating the results of an exemplary calorimetric measurement (ARC measurement) with potentially suitable additives;

(5) FIG. 3 is a graph illustrating the results of a further ARC measurement with further variations in respect of the additive;

(6) FIG. 4 is a graph illustrating the results of a further ARC measurement with further variations in respect of the additive;

(7) FIG. 5 is a graph illustrating the results of a further ARC measurement with further variations in respect of the additive; and

(8) FIG. 6 is a graph illustrating the results of a further ARC measurement with further variations in respect of the additive.

DETAILED DESCRIPTION

(9) FIG. 1 illustrates, using a block diameter, an exemplary embodiment of a method for the surface treatment of workpieces. By way of example, the method may comprise a material-depleting and/or material-levelling grinding treatment, brushing treatment, blasting treatment, machining treatment or polishing treatment of metallic workpieces.

(10) In a step S10, the method comprises the provision of a treatment tool, such as a grinding disk, brushing disk, blasting system, machining tool or polishing disk. The treatment tool is, by way of example, of disk-like design and is accommodated on a spindle which is coupled to a drive. The treatment tool is designed to accommodate a surface treatment composition. For this purpose, the treatment tool may be configured with at least some absorbency and/or porosity. The treatment tool may for example comprise fibers, woven fabrics and/or sponge-like materials.

(11) A further step S12 relates to the provision of an abrasive medium for the surface treatment. By way of example, this may be a grinding composition, brushing composition, blasting medium, cutting material or polishing composition. The medium may take the form, for example, of a solid, solid paste or emulsion. The medium comprises typically abrasive constituents, for instance granular abrasives, cutting materials and/or blasting medium, which may be embedded in a carrier material, such as a lipid-based carrier material. The step S12 may further comprise application of the medium to the treatment tool provided in step S10. This may be done manually or automatically. Depending on the nature of the surface treatment composition, the application may involve spraying, pouring, printing, and similar processes.

(12) A further step S14 involves the supplying of a workpiece having a surface to be treated. The workpiece is at least partially metallic and is, in certain embodiments, fabricated from light metals or nonferrous metals, such as from aluminum, magnesium, zinc or titanium, or from alloys containing aluminum, magnesium, titanium and/or zinc. The supplying may comprise automatic or manual supplying. The workpiece is typically supplied to a treatment tool arranged with a fixed location but coupled to a drive. This, however, is not to rule out the supplying of the treatment tool onto the workpiece, according to alternative exemplary embodiments. In general the step S14 may include a relative movement between the workpiece and the treatment tool.

(13) As well as workpiece-guided treatment it is also possible to conceive of tool-guided treatment. In that case the workpiece is fastened in a corresponding mount and then treated by a multi-dimensionally pivotable head of the tool; accordingly, the “supplying” should be understood in relative terms. In other words, this may be a tool-guided or else a workpiece-guided treatment.

(14) This is followed by a step S16, which comprises the actual surface treatment of the workpiece. Here, material is removed from the workpiece, for instance chips or other small particles, which can form dust. Furthermore, the treatment gives rise generally to abraded material of the treatment tool, in the form, for example, of fiber residues, composed of cotton shreds and/or dusts, for instance. In addition there is further waste, owing to the surface treatment composition. This may relate on the one hand be part of the composition which has not even been involved in the treatment itself, but instead has been thrown away from the treatment tool. It may further relate to portions of the surface treatment composition which have made contact with the workpiece. The waste generated during the course of the surface treatment hence comprises diverse constituents.

(15) Waste products arising in the course of the surface treatment are processed by wetting in a step S18. This may involve removal of the waste from the location of the treatment itself. This may be done, for example, by suction withdrawal units which operate continuously. Generally, however, waste products remain at the location of the processing, having not been sucked up. These waste products can be removed mechanically, such as manually by regular cleaning, for example. According to at least some exemplary embodiment examples, the step S18 comprises a treatment of the waste products in a wet separator. Other modes of waste treatment and waste processing are conceivable. It is, for example, not unusual for the waste products to be put into interim storage, in order, for instance, to collect sufficiently large quantities, which can then be disposed of.

(16) A further exemplary embodiment of the processing of waste products involves the briquetting of the waste. In this case the waste is compressed and so dewatered, and at the same time oxygen is withdrawn from the waste. In this connection, further binder additions are frequently added to the waste.

(17) A further step S20 relates to the disposal of the waste products. This requires specialist knowledge and specific operations, and so is often done by qualified external firms.

(18) Both during and after the treatment there is a risk in principle of self-ignition of the waste, or of fire due to external ignition. In theory this may even take place at the location of treatment itself. However, this risk has been significantly reduced by safety provisions, which prescribe, for instance, the use of suction withdrawal units. Now and then, however, it has been observed that collective wastes tend towards spontaneous self-ignition. The risk of this rises in principle with the quantity of waste and of the storage time, and with the associated evaporation of water. Other influencing factors have already been explained above.

(19) In the context of the present disclosure, a proposal is made to add or admix, in at least one component step of the method, an additive which ultimately lowers the self-ignition tendency of the wastes.

(20) Steps S22, S24 and S26 relate in each case to the admixing of the additive. Steps S22, S24 and S26 represent different possibilities for the admixing of the additive. Steps S22, S24 and S26 can be implemented. This does not, however, rule out the utilization of two or more of the steps S22, S24 and S26 for admixing the additive. What is essential is that the additive is detectable at least after the processing of the waste products (step S18).

(21) For example, in the step S22, the additive can be added during the provision of a treatment tool (step S10). Hence it is possible to conceive of the treatment tool being treated accordingly. The additive may be introduced into the waste, for instance, via the abraded disk material which is formed during the treatment and which forms a constituent of the resultant waste. Alternatively, the additive may be present in solution in the solvent which is used in the processing of the waste products.

(22) The additive, furthermore, may be added in accordance with step S24, for example, as part of the provision of the surface treatment composition (step S12). In other words, the compositions utilized, such as grinding composition, brushing composition, blasting medium, coating material or polishing composition, may be provided with the additive. The surface treatment composition forms a constituent of the resultant waste, and so the additive may ultimately be available there in order to lower the reactivity of the waste, especially of metal shavings and metal particles in the waste.

(23) Furthermore, in accordance with step S26, for example, the additive may be introduced into the waste as part of the processing of the latter (step S18). This may involve the waste being thoroughly mixed with the additive. The additive may also be added during the briquetting of the waste products.

Working Examples

(24) In the course of the surface treatment, for instance in the case of polishing, various polishing compositions are employed, depending on the material, the desired surface quality, and other factors. The wastes resulting in this case consist, for example, of the remnants of the polishing composition, cotton fibers of the polishing disks, and also the abraded metal generated from the material. This waste is drawn off by suction, for example, passed through wet separators, and subsequently stored. In the course of storage there are occasionally instances of spontaneous self-ignitions of the wastes, which need to be brought under control through the deployment of the fire service.

(25) It has been possible to show that the trigger for this self-ignition is the heat of reaction associated with the oxidation of abraded light-metal particles. In the trials described below additives suitable for suppressing or at least attenuating this reaction have been investigated.

(26) The measurement method used was Accelerating Rate calorimetry (ARC). Accelerated Rate calorimetry (ARC) is a thermal analytical method in which a sample is stored in a controllable oven. In the method, the temperature of the sample is measured and the oven is run in accordance with the sample temperature, so that there is no heat flow whatsoever from the sample into the oven or vice versa. Accordingly the conditions prevailing are at least approximately adiabatic.

(27) In this way it is possible to simulate the situation inside a large sample, in which the loss through thermal conduction to the surroundings is virtually zero and the heating takes place exclusively as a result of the chemical reactions in the sample. Because the rate of chemical reactions is temperature-dependent, the resultant heat of reaction raises the reaction rate and hence increases the heating within the interior of the sample. There is therefore a self-reinforcing effect, and accelerated heating may occur.

(28) During a measurement, the sample is initially brought to a defined starting temperature and held there. If no temperature increase is recorded within a given time window, the oven temperature is raised by a fixed amount and then the sample as well is observed for a temperature increase. This procedure is continued until the sample exhibits intrinsic heating.

(29) From this moment on, the oven automatically regulates itself to the actual sample temperature. This is continued until either the intrinsic heating comes to a standstill (as a result of complete reaction, for example) or until upper pressure or temperature limits are reached.

(30) The measurement is plotted as the Self Heating Rate (SHR in ° C./min) against the temperature (in ° C.). From the shape of the curve here it is possible to ascertain whether there is accelerated heating and, if so, the temperature at which it begins.

1. Preparatory Work

(31) In a first trial the aim was to find out which compounds are suitable for reducing the self-ignition tendency of polishing composition waste. First of all, the salts sodium fluoride and sodium carbonate were chosen as potentially suitable candidates.

(32) The raw material used was real polishing composition waste arising in the surface treatment of aluminum-containing workpieces. As part of the surface treatment, the waste products arising were collected without prior processing. The waste, therefore, was not processed in a wet separator, and consequently was largely dry.

(33) The first trials involved preparatory work in accordance with the steps below, before an ARC measurement was carried out: 1. Dissolving the salt in question (amount in % based in each case on 10 g of polishing composition waste) in 200 ml (milliliter) of deionized water; 2. Stirring 10 g of polishing composition waste into the solution, leaving it to stand, and re-agitating; 3. Allowing the salt to act (usually 24 hours); 4. Isolating polishing composition waste by filtration and washing it with distilled water; 5. Drying for 24 h in a fume cupboard at room temperature; and 6. Storage, pending the ARC measurement, in a desiccator under molecular sieve.

(34) Step 1 in conjunction with step 2 in this case simulates processing in a wet separator, which is frequently used in the case of surface treatment. Accordingly, the findings obtained can also be applied to wastes which have passed through a wet separator.

(35) FIG. 2 shows the results of the trials. All of the salts (NaF, Na.sub.2CO.sub.3) compared with water (serving as reference), exhibit less self-heating. The self-heating of the reference can be seen in the region starting at 230° C. In this first trial it was found that sodium carbonate and sodium fluoride as additives used are able to lower the self-ignition tendency of the waste. Impressively it was found that, within the concentration ranges chosen, it was barely possible to observe any measurable, potentially critical self-heating of the samples.

(36) Besides the ARC measurement, a DSC measurement (Differential Scan calorimetry) was carried out in parallel (not shown in the figures). The result of this measurement was that all of the salts lower the energy content (J/g) of the peak (reference around 200° C.). Additionally there is an increase in the onset temperature, this being the temperature at which there is an exothermic response.

(37) On the basis of these findings, further trials were conducted with sodium carbonate and sodium fluoride. In these trials, different additive concentrations and different exposure times were investigated.

2. Varying the Concentrations and Exposure Times of the Salts

(38) In a second trial, the effect of different concentrations and exposure times of the salts on the waste was investigated. The trial procedure was analogous to that described in section 1.

(39) The results of this ARC measurement are shown in FIG. 3.

(40) FIG. 3 provides an overall view of the various self-heating processes on part of the samples. All of the samples admixed with additives as per the disclosure exhibit lower self-heating than the untreated sample. In the region starting at 230° C., a 1% NaF sample with 86 h exposure time exhibits greater self-heating at 1% Na.sub.2CO.sub.3 sample with 72 h exposure time. Additionally, the 10% Na.sub.2CO.sub.3 sample with 6 h exposure time likewise exhibits higher self-heating than the aforementioned 1% Na.sub.2CO.sub.3 sample with 72 h. This shows an influence of the exposure time as well as the influence of the salt concentration.

(41) In order clearly to delineate these influences, the NaF and Na.sub.2CO.sub.3 samples were repeated once again with identical exposure times of 24 hours. These results are shown in FIG. 4. In relation to the reference, the self-heating is reduced to 56.5% (carbonate) and 39.1% (fluoride).

3. Polishing Compositions Comprising a Salt Composed of Carbonate/Halogen Anion

(42) On the basis of the findings obtained from the trials described above, in the next step a modified polishing emulsion was prepared, with the respective salts sodium fluoride, sodium carbonate, and potassium carbonate. These polishing compositions were used to carry out polishing trials with a robot. The resultant wastes were produced in a wet separator, and so the polishing waste was in a wet form. The trials encompassed the following steps, before an ARC measurement was carried out: 1. Stir 10 g of polishing waste into 200 ml of distilled water, leave to stand, re-agitating; 2 Rest solution for 24 h; 3. Isolate residue by filtration and wash with distilled water; 4 Dry residue for 24 h in a fume cupboard at room temperature; and 5 Store, pending ARC measurement, in a desiccator under molecular sieve.

(43) The results of these trials are shown in FIG. 5.

(44) In the trials it is apparent that in this set-up, the activity of sodium fluoride is poorer than that of the different carbonates. Further, in the case of both the reference sample and the fluoride sample, the curves toward the end become steeper as the temperature rises, whereas the carbonates toward the end show a somewhat flattening curve. Here, accordingly, it was possible to inhibit the self-heating and possibly even bring it to a standstill at higher temperatures.

(45) In a further trial, therefore, the reference was admixed with 1 or 2 wt % sodium carbonate and investigated. FIG. 6 summarizes all of the carbonate samples. There is clear decrease apparent in the self-ignition tendency from the reference to the samples with 1 wt % carbonate. The sample with 2 wt %, as well as the lower self-heating, exhibits a peak at around 270° C., from which the self-heating decreases again. This sample shows no self-accelerated heating. According to these measurements, a higher concentration of additive (2% instead of 1%, for example) is preferential in terms of the inhibitory properties.

4. Conclusion

(46) In the experimental trials, fluoride and carbonate proved to be suitable additives. On direct incorporation into the formulation, carbonate exhibits a better effect than fluoride, which in preliminary trials with older polishing composition waste appeared to be more suitable. The selection of the cation (sodium or potassium) does not appear to have any influence on the inhibitory activity of the additive, and can be optimized as part of the formulation work. Higher concentrations of additive may increase the safety of the wastes, as a result of reduced self-heating.

(47) It has been possible, furthermore, to show that the self-ignition tendency can be lowered even in the case of wastes obtained in blasting processes or machining processes. These wastes typically consist primarily of metal dust or shavings, blasting medium, and water. As a result of the addition of the additive, the metals undergo reaction, and so it is widely possible to limit the generation of the highly ignitable hydrogen and, accordingly, the self-ignition tendency of this waste as well is lowered.